Conventionally, Long Term Evolution (LTE) standardized in 3rd Generation Partnership Project (3GPP) is becoming widely used as a new wireless communication method. In LTE, providing Voice over LTE (VoLTE) that is a voice service using the Internet protocol Multimedia Subsystem (IMS) is being prepared as a multimedia service based on the Internet Protocol (IP). In VoLTE, in addition to a default bearer that is a communication path used for general data, an IMS call process Session Initiation Protocol (SIP) signaling bearer (hereinafter, referred to as an “IMS signaling bearer”) that is a communication path used for controlling voice data is used.
Each of the bearers is, for example, the bearers defined in TR 23.854 (Sec 6.1.3.2.1), TS 23.203 (Sec 6.2.4), and the like in 3GPP. Unlike a default bearer used for user data communication (hereinafter, simply referred to as a “default bearer”), a dedicated access point network (APN: Access Point Name) is provided with an IMS signaling bearer. The APN is specified to enable to establish emergency communication with a local agency in an international roaming network without passing through the home network. Specifically, the wireless communication system provides an incoming call service for a mobile station by continuously setting the IMS signaling bearer described above between the APN and a mobile station (UE: user equipment).
Patent Document 1: International Publication Pamphlet No. WO 2008/096527
However, in the technology described above, high-quality voice communication is possible but there is the following problem. For example, the wireless communication system always needs to ensure the resource in order to maintain an IMS signaling bearer. Furthermore, if an address conversion device (NAT: Network Address Translator) is present between the Evolved Packet Core (EPC) and an IMS call process server (CSCF: Call Session Control Function), the wireless communication system performs periodical keep alive communication in order to maintain address conversion information. Consequently, although no transmission addressed to a mobile station is present, the wireless resource between the mobile station and a base station is consumed.